“Thus you shall separate the Levites from among the people of Israel, and the Levites shall be mine.
We read before of the separating of the Levites from among the children of Israel when they were numbered, and the numbering of them by themselves (Num 3:6, Num 3:15), that they might be employed in the service of the tabernacle. Now here we have directions given for their solemn ordination (Num 8:6), and the performance of it, Num 8:20.
Commenting on Numbers 8:5-26
Thus shalt thou separate the Levites from among the children of Israel,.... By sprinkling the water of purification upon them; by offering sacrifices for them; by presenting them before the Lord, with the hands of the people of Israel put upon them; by offering and waving them before the Lord, and by setting them before Aaron and his sons, as their ministers: and the Levites...
and the Levites shall be mine--that is, exempt from all military duty or secular work--free from all pecuniary imposition and wholly devoted to the custody and service of the sanctuary.